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The total amount spent on digital advertising in 2012 was just more than $104 billion. That total is expected to grow to $116.8 billion in 2013, and Google Inc. (NASDAQ: GOOG) will get the lion's share.

According to the latest estimates from research firm eMarketer, Google will claim about 31.5% of global ad revenues for 2012 and more than 33% in 2013. The revenues reflect both desktop and mobile advertising. eMarketer figures Google's digital advertising revenue at $32.73 billion in 2012 and expects the search giant to post revenues of $38.83 billion this year.

Trailing way behind in second place is Facebook Inc. (NASDAQ: FB) with 4.11% of 2012 global digital ad revenue ($4.28 billion) and an 2013 estimate for a 5.04% share ($5.89 billion). Yahoo! Inc. (NASDAQ: YHOO) is third with a 3.37% share in 2012 and an estimate for 3.1% this year.

Looking just at mobile Internet advertising revenues, Google raked in $4.61 billion of a global total of $8.8 billion in mobile ad spending. Only 'other' posted revenues higher than $1 billion.

In 2013, eMarketer estimates the mobile Internet will generate a total of $15.82 billion, of which Google will again claim more than half - $8.85 billion. Facebook Inc. took in just $470 million in 2012, but is projected to more than triple its take in 2013 to $2.04 billion.

It's a different story when it comes to growth rates, of course, where being huge is a disadvantage. Here's eMarketer's story:

While both Google and Facebook are increasing revenues at faster rates than the overall digital ad spend market, dramatic increases in ad revenues are more difficult for companies with such high earnings. Twitter will post the fastest growth rate in worldwide ad revenues among the companies eMarketer analyzed, with a 102.2% increase expected this year after a 106.7% increase in 2012. That's compared with 12.3% growth in total digital ad spending projected for 2013, and 20.4% growth estimated for 2012.